1. Field of the Invention
The present invention relates to a method of energizing an AC discharge plasma display panel for use as a large-area flat display panel with a personal computer, a workstation, or a wall television set.
2. Description of the Relates Art
Plasma display panels (also referred to as xe2x80x9cPDPxe2x80x9d) are classified according to operating principles into DC discharge PDPs in which electrodes are exposed to a discharge gas and cause a discharge only when a voltage is applied, and AC discharge PDPs in which electrodes are covered with a dielectric layer and cause a discharge while being not exposed to a discharge gas. Discharge cells of the AC discharge PDPs have a memory function because of a charge storage action of the dielectric layer.
One general AC discharge color PDP will be described below with reference to FIG. 1 of the accompanying drawings. FIG. 1 shows a fragmentary cross section of the AC discharge color PDP. As shown in FIG. 1, the AC discharge color PDP comprises a front substrate 10 of glass and a back substrate 11 of glass which are spaced from each other with a space defined therebetween.
Scanning electrodes 12 and common electrodes 13 which are spaced from each other by given distances are disposed on the front substrate 10. The scanning electrodes 12 and the common electrodes 13 are covered with an insulating layer 15a which is covered with a protective layer 16 of MgO or the like that protects the insulating layer 15a from electric discharges.
Data electrodes 19 which extend perpendicularly to the scanning electrodes 12 and the common electrodes 13 are disposed on the back substrate 11. The data electrodes 19 are covered with an insulating layer 15b which is coated with a phosphor layer 18 that converts an ultraviolet radiation generated by electric discharges into visible light for display.
Partitions 17 extend between the insulating layers 15a and 15b, providing a discharge space 20 therebetween. The partitions 17 define pixels for displaying images on the PDP. The discharge space 20 is filled with a discharge gas which comprises a mixture of He, Ne, Xe, etc.
FIG. 2 of the accompanying drawings shows the layout of the electrodes in the color PDP shown in FIG. 1.
In FIG. 2, the color PDP has m scanning electrodes Si (i=1, 2, . . . , m) 12 extending as rows, n data electrodes Dj (j=1, 2, . . . , n) 19 extending as columns, the scanning electrodes Si and the data electrodes Dj intersect with each other at the pixels, and m common electrodes Ci (i=1, 2, . . . , m) 13 extending as rows parallel to the scanning electrodes Si and paired with the scanning electrodes Si. The phosphor layer 18 has a plurality of areas aligned respectively with the pixels 14 and coated with different colors of R, G, B for enabling the PDP to display color images.
A process of energizing the conventional color PDP shown in FIGS. 1 and 2 will be described below with reference to FIG. 3 of the accompanying drawings. FIG. 3 is a timing chart of drive voltages which are applied to the electrodes of the conventional color PDP.
First, erasing pulses 21 are applied to all the scanning electrodes 12 to turn off all the pixels which have previously emitted visible light.
Then, preliminary discharge pulses 22 are applied to the common electrodes 13 for forcibly discharging all the pixels to emit visible light. Thereafter, preliminary discharge erasing pulses 23 are applied to all the scanning electrodes 12 to turn off a preliminary discharge at all the pixels. The preliminary discharge allows a subsequent writing discharge to be effected with ease.
After the preliminary discharge is turned off, scanning pulses 24 are applied at different times to the scanning electrodes (S1xe2x88x92Sm) 12, and data pulses 27 representative of data to be displayed are applied to the data electrodes (D1xe2x88x92Dn) 19 in timed relation to the scanning pulses 24. Diagonal lines indicated in the data pulses 27 show that the presence or absence of data pulses 27 is determined according to whether there is data to be displayed or not. If a data pulse 27 is applied to a pixel when a scanning pulse 24 is applied thereto, then a writing discharge occurs at the pixel in the discharge space 20 between the scanning electrode 12 and the data electrode 19. If no data pulse 27 is applied to a pixel when a scanning pulse 24 is applied thereto, then no writing discharge occurs at the pixel.
At a pixel where a writing discharge occurs, a positive charge called a wall charge is collected in the insulating layer 15a on the scanning electrodes 12. At this time, a negative wall charge is collected in the dielectric layer 15b on the data electrodes 19. The positive wall charge in the insulating layer 15a and first negative sustaining pulses 25 applied to the common electrodes 13 are superposed thereby to generate a first sustained discharge. When the first sustained discharge is generated, a positive wall charge is collected in the insulating layer 15a on the common electrodes 13, and a negative wall charge is collected in the insulating layer 15a on the scanning electrodes 12. Second sustaining pulses 26 applied to the scanning electrodes 12 are superposed on the potential difference between these wall charges thereby to generate a second sustained discharge. In this manner, the potential difference between wall charges developed by an xth sustained discharge and (x+1)th sustaining pulses are superposed thereby to continue sustained discharges. The number of times that a sustained discharge is continued controls the amount of visible light emitted from the pixels.
The voltage of the sustaining pulses 25, 26 is adjusted such that the voltage of these pulses alone will not develop a discharge. At a pixel where no writing discharge has been developed, there is no potential due to a wall charge before the first sustaining pulses 25 are applied. At such a pixel, therefore, no first sustained discharge is produced even when the first sustaining pulses 25 are applied, and no subsequent sustained discharge will be produced.
Each of the erasing pulses 21, the preliminary discharge pulses 22, the preliminary discharge erasing pulses 23, the scanning pulses 24, the sustaining pulses 25, 26, and the data pulses 27 described above has heretofore been a rectangular pulse whose rise and fall times are 1 microsecond or less each as shown in FIG. 4A.
When the color PDP develops a discharge with the rectangular pulse shown in FIG. 4A, a discharging current shown in FIG. 4B flows in an electrode to which the rectangular pulse is applied. The discharging current starts to flow several hundreds nanoseconds after the application of the rectangular pulse, reaches a peak level another several hundreds nanoseconds thereafter, subsequently sustains for several hundreds of nanoseconds, and is then terminated.
The time from the application of the pulse to the start of the discharging current, the time to the peak level, and the subsequent time for which the discharging current is sustained depend on the composition of the discharge gas, the composition of the dielectric layer, the thickness of the dielectric layer, the composition of the electrodes, the sizes of the electrodes, and the size of the discharge space.
For example, a phosphor material has a discharge emission efficiency of about 80 lm/W, and a PDP which is energized by the above conventional process has a much lower discharge emission efficiency of about 1 lm/W. Therefore, the PDP needs to consume a large amount of electric energy in order to increase the emission luminance.
It is therefore an object of the present invention to provide a method of energizing a plasma display panel to increase emission efficiency with sustained discharges for thereby reducing electric energy consumption.
To achieve the above object, there is provided in accordance with the present invention a method of energizing a plasma display panel having a plurality of scanning electrodes arranged as rows and a plurality of data electrodes arranged as columns, comprising the steps of applying a scanning pulse voltage to the scanning electrodes, applying a data pulse voltage to the data electrodes in synchronism with the scanning pulse voltage for controlling turning-on/off of displayed data, and thereafter, applying a sustaining pulse voltage of a waveform having repetitive units each including a preceding high potential difference of a short duration and a subsequent low potential difference of a long duration, alternately to two electrodes selected from the scanning electrodes, the data electrodes, and common electrodes arranged as rows independently of the scanning electrodes, for thereby keeping a sustaining discharge only in cells where the displayed data is turned on.
The above method allows sustaining pulses to be optimized in waveform for enabling the plasma display panel to display images with increased emission efficiency, increased emission luminance, and reduced electric energy consumption.
The short duration of the preceding high potential difference may be shorter than a delay time from the application of the sustaining pulse voltage until a gas discharging current is maximized.
The short duration of the subsequent low potential difference and a setting of the subsequent low potential difference may be determined to keep the sustaining discharge even in the absence of the duration of the preceding high potential difference.
Each of the repetitive units may include a high voltage pulse of a short duration applied to one of the two electrodes and a low voltage pulse, in opposite polarity to the high voltage pulse, of a long duration applied to the other of the two electrodes after the high voltage pulse has ended.
Each of the repetitive units may include a pulse of a short duration applied to one of the two electrodes and a low voltage pulse, in opposite polarity to the pulse, of a long duration applied to the other of the two electrodes at the same time that the pulse is applied to the one of the two electrodes.
Each of the repetitive units may include a high voltage pulse of a long duration applied to one of the two electrodes and a low voltage pulse, in the same polarity as the high voltage pulse, of a long duration applied to the other of the two electrodes with a delay equal to the short duration of the high voltage pulse, after the application of the high voltage pulse.
A portion of a plurality of sustaining pulses for producing a sustaining discharge may have the waveform of the sustaining pulse voltage.
A plurality of sustaining pulses applied to one of a pair of electrodes for producing a sustaining discharge may have the waveform of the sustaining pulse voltage.
The preceding high potential difference may be generated by an overshoot in excess of the amplitude of the sustaining pulse voltage.
According to the present invention, there is also provided a method of energizing a plasma display panel having a plurality of scanning electrodes arranged as rows and a plurality of data electrodes arranged as columns, comprising the steps of applying a scanning pulse voltage to the scanning electrodes, applying a data pulse voltage to the data electrodes in synchronism with the scanning pulse voltage for controlling turning-on/off of displayed data, and thereafter, applying a sustaining pulse voltage of a waveform having repetitive units each including a preceding low voltage and a subsequent high voltage of a long duration for producing a sustaining discharge, alternately to two electrodes selected from the scanning electrodes, the data electrodes, and common electrodes arranged as rows independently of the scanning electrodes, for thereby keeping a sustaining discharge only in cells where the displayed data is turned on.
The above method also enables the plasma display panel to display images with increased emission efficiency, increased emission luminance, and reduced power consumption.
The preceding low voltage may be of a level and a duration which are selected to fail to produce a sustaining discharge.
The preceding low voltage and the subsequent high voltage may be successively applied.
Each of the repetitive units may include a reference potential or a potential lower than the preceding low voltage, between the preceding low voltage and the subsequent high voltage.
A portion of a plurality of sustaining pulses for producing a sustaining discharge may have the sustaining pulse voltage.
The sustaining pulse voltage may be applied to one of a pair of electrodes for generating a sustaining discharge.
The above and other objects, features, and advantages of the present invention will become apparent from the following description based on the accompanying drawings which illustrate an example of preferred embodiments the present invention.